systray.xml

<?xml version="1.0" encoding="UTF-8" ?>
<templates>
   <t t-name="theme_systray">
       <li class="new_icon">
           <label class="theme_sdn" style="margin-bottom:0px;" title="Change backend theme">
               <t t-if="widget.is_admin">
                  <div class="icon_div sdn_systray_icon" groups="base.group_system">
                      <div class="toggle-icon"
                           style="font-size: 1.9rem !important; margin: auto 11px !important;">
                          <i id='theme_sdn' class="fa fa-paint-brush" role="img" aria-label="Theme"/>
                      </div>
                  </div>
               </t>
           </label>
       </li>
   </t>
</templates>